The present invention relates to a photometry device applicable to an SLR (Single Lens Reflex) camera, and more particularly to a photometry device with which exposure errors due to a difference of reflectivity of objects having different colors can be compensated.
Recently, in most of cameras, reflection type photometry devices are employed. The reflection type photometry device receives the light, which is reflected by an object and passed through an observing optical system of a camera, using a light receiving element, determines the brightness of the object based on the output of the measured value, and then calculates the exposure value of the camera based on the measured brightness. However, this type of the photometry device cannot detect the color of the object because of its structure. Accordingly, in such a device, the reflectivity of an object is generally assumed to be 18% and the exposure parameter is determined on this assumption. Therefore, regarding a whitish object whose reflectivity is greater than 18%, the determined brightness is greater than the actual brightness. If the camera controls an exposure operation based on the determined exposure value, the object is under exposed. A dark object whose reflectivity is less than 18% is measured to have a lower brightness. Therefore, such an object is over exposed. The difference of the reflectivity of the object may also occur depending on the color of the object.
For example, when the color of an object is yellow, the reflectivity maybe up to 70%. In such a case, if the standard reflectivity is assumed to be 18%, the exposure value is approximately 2 Ev lower than necessary. If the object color is blue, the reflectivity is approximately 9%. In this case, the object is over exposed by approximately 1 Ev greater than necessary.
Therefore, in the conventional photometry device, the photographer is required to guess the reflectivity of the object. Then, based on the reflectivity determined by the photographer, the exposure is controlled such that, if the object is a whitish or yellowish one having a relatively high reflectivity, it is to be overexposed, and if the object is a blackish or bluish one having a relatively low reflectivity, it is to be underexposed. With this operation, the above-described defects may be solved.
However, accurately guessing the reflectivity of the object and controlling the exposure can be done only by experienced and skilled photographers. It is impossible to require all the photographers to do such an operation. Further, it is not preferable that a manual operation of the photographer is required for exposure. Further, if such a manual operation is required, cameras become unsuitable for the recent trend of automatic photographing.
It may be possible to measure the color of the object, and perform exposure compensation based on the reflectivity corresponding to the measured color. If such a control is performed, an appropriate exposure value seems to be obtained automatically regardless of the color of the object. To perform such an operation, a plurality of photometry sensors for performing colorimetry may be provided inside the camera for selectively measuring different portions of the object, and a so-called TTL colorimetry may be performed. That is, light passed through a photographing lens of the camera is received by the plurality of sensors.
When such a structure is adopted, however, the spectral reflection characteristics of the object and the spectral radiant characteristic of an external light source are overlapped when the colorimetry is performed. Therefore, due to the spectral radiant characteristics of the external light source illuminating the object, it becomes difficult to measure the object color accurately. Then, the compensation amount of the exposure value includes errors, and the appropriate exposure may not be achieved.
It may be possible to measure the spectral radiant characteristic of the external light source independently, and compensate for the colorimetry result using the spectral radiant characteristic of the external light source. However, depending on photographing conditions, the spectral radiant characteristic of the external light source may not be measured accurately. For example, when a photographing magnification is relatively large, or a distance between the camera and an object is relatively small, as in a macro photographing, the light reflected by the object is also received by a photometry system for the external light source. In such a case, the colorimetry result cannot be compensated for correctly, and therefore, the appropriate exposure amount may not be determined.
It is therefore an object of the invention to provide an improved photometry device which optimizes the effectiveness of a light source compensation value, which is obtained based on the spectral radiant characteristic of an external light source, in accordance with a photographing condition, so that an exposure compensation amount is calculated in accordance with the colorimetric compensation value, and thereby appropriate exposure values can be obtained regardless of a difference of photographing conditions as well as the reflectivity of the object.
For the above object, according to the invention, there is provided a photometry device for a camera, which is provided with a normal light sensor that performs photometry with respect to an object, an exposure amount determining system that determines an exposure amount of the object in accordance with an output of the normal light sensor, a plurality of colorimetric sensors that detect a color of the object by performing colorimetry with respect to an image of the object which is formed by a photographing lens of the camera, the plurality of colorimetric sensors having spectral sensitivity characteristics that are different from each other, an external light sensor that measures an external light illuminating the object at spectral sensitivity characteristics respectively corresponding to the plurality of colorimetric sensors, a light source color compensation amount determining system that determines light source color compensation amount in accordance with the output of the external light sensor, a light source effect compensation system that compensates for the outputs of the colorimetric sensors in accordance with the light source color compensation amount, a colorimetry compensation amount determining system that determines a color of the object based on the output of the colorimetric sensors as compensated by the light source effect compensation system, and then determines a colorimetric compensation amount based on the determined color, an exposure amount compensation system that compensates for the exposure amount determined by the exposure amount determining system in accordance with the colorimetric compensation amount. In such a device, the light source color compensation amount determining system changes the light source color compensation amount in accordance with an object distance.
Alternatively, the light source color compensation amount determining system changes the light source color compensation amount in accordance with the magnification of the photographing lens.
Optionally, a predetermined fixed value is used as the light source color compensation amount if the photographing magnification exceeds a predetermined photographing magnification range or the object distance is smaller than a predetermined fixed distance.
Further optionally, a value intermediate the light source color compensation amount as determined by the light source color compensation amount determining system and a predetermined fixed value is used as the light source color compensation amount if the photographing magnification exceeds a predetermined photographing magnification range or the object distance is smaller than a predetermined fixed distance.
Further, the light source data corresponding to the output of the light source photometry system is stored in a storing system, and the fixed value is obtained in accordance with the data stored in the storing system.
Still optionally, a condition where the photographing magnification exceeds a predetermined photographing magnification range or the object distance is smaller than a predetermined fixed distance includes a condition where the camera operates in a macro photographing mode.
Further optionally, the normal light sensor and the plurality of colorimetric sensors meters light reflected by the object and passed through an optical system of the camera, and wherein the external light sensor receives light which is not passed through the optical system of the camera.
Furthermore, the normal light sensor includes a normal light photometry sensor, the spectral sensitivity characteristic of which has a peak sensitivity at a wavelength within a range from 500 nm through 600 nm, the plurality of colorimetric sensors include a blue light photometry sensor for metering blue light component, a green light photometry sensor for metering green light component, and a red light photometry sensor for metering red light component, and the external light sensor includes a photometry sensor having photometry areas for metering blue, green and red light components, respectively.
In this case, the light source effect compensation system may compensate for at least two of the outputs of the colorimetric sensors corresponding to three primary colors of green, blue and red in accordance with the light source color compensation amount.
Further, the plurality of calorimetric sensors and the normal light sensor may include photometric elements having the same photometric characteristics.
In this case, the green light sensor may be used as the normal light sensor, the output of the green light sensor being used as the output of the normal light sensor.
Optionally, each of the normal light sensor and the plurality of colorimetry sensors has divided photometry areas, the exposure amount determining system and exposure compensation amount determining system determining the exposure amount and the exposure compensation amount in accordance with the output of each of the divided photometry areas.
In this case, the colorimetric compensation amount determining system may judge the color of the object at each of the divided photometry areas, determine the colorimetric compensation amount for each of the divided photometry areas, and determine a colorimetric compensation amount with respect to an entire object based on the calorimetric compensation amounts for the divided photometry areas.
Alternatively, the colorimetric compensation amount determining system may determine a calorimetric compensation amount for each of the divided photometry areas, and add a colorimetric compensation amount for each of the photometry areas to the photometry output for each of the divided photometry areas.